National Transportation Safety Board 

Washington, D.C. 20594 

The Honorable Michael P. Huerta 

Acting Administrator 

Federal Aviation Administration 

Washington, D.C. 20591 

Safety Recommendation 

Date: FEB 2 4 2012 

In reply refer to: A-12-7 

Since 2000, the National Transportation Safety Board (NTSB) has examined numerous 

Engine Components, Inc. (ECi) reciprocating engine cylinder assemblies that failed due to 

fatigue cracking that initiated in the root of the cylinder head thread, eventually resulting in loss 

of compression and/or separation of the cylinder head into two pieces. I These failures involved 

new assemblies installed on Lycoming and Teledyne Continental Motors (TCM)2 engines, and 

many resulted in fatal accidents. Although the Federal Aviation Administration (FAA) has issued 

several airworthiness directives (AD) applicable to certain new ECi cylinder assemblies used on 

Lycoming and TCM engines to address this issue, similar fatigue failures in other new ECi 

cylinder assemblies installed on TCM engines have been identified but are not covered by an 

existing AD. Because fatigue cracking and separation of cylinder assemblies in piston-engine 

aircraft is a serious safety issue, this letter recommends corrective action for certain new ECi 

cylinders used on TCM engines. 

Reciprocating engine cylinder assemblies consist of two major parts, the cylinder barrel 

and the cylinder head. ECi cylinder heads are manufactured from an aluminum alloy casting, and 

house the intake and exhaust valves, with their respective seats, guides, and spark plugs. ECi 

cylinder barrels are typically manufactured from an alloy steel forging and have a smooth bore 

that houses the piston. The cylinder head and barrel are joined by heating the cylinder head to 

about 650 0 F then screwing it onto the cylinder barrel until specific surfaces make contact. As 

the cylinder head cools and shrinks onto the cylinder barrel, an interference fit is produced, 

locking the parts together at the threads and at an adjacent plain diameter, which is commonly 

referred to as a shrink band (shrink bands are features on the barrel and in the cylinder head; see 

figure 2). On new cylinder assemblies, the barrel mounting flange and cylinder mounting holes 

in the flange are machined after assembly to ensure the cylinder's proper alignment on the 

engme case. 

I Cylinder assemblies examined include those in connection with the following NTSB case numbers: 

ENG07WA032 (three cylinders), ENG07SA033, and WPR09SA476. 

2 Teledyne Continental Motors became Continental Motors, Inc. in April 20 II. 

8383 
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In most of the cases examined by the NTSB, the fatigue cracks in the cylinder heads 

initiated at the root of the thread that was engaged with the first (uppermost) thread on the 

cylinder barrels, as shown in figure 1 and indicated by the yellow line in figure 2. The fatigue 

cracks propagated outwards through the cylinder head wall to emerge between the third and 

fourth or the fourth and fifth cooling fin, depending on the engine model. The fatigue cracks 

initiated at multiple locations, typically near the intake or exhaust valve side of the cylinder 

heads and, with engine use, propagated through the head thickness. Once the fatigue cracks 

propagated though the thickness of the cylinder wall, the cylinders lost compression, with a 

resulting reduction in or total loss of thrust. When the fatigue cracks reached a critical size, the 

cylinder heads fractured and separated at the fatigue location, with the lower portion remaining 

attached to the barrels, resulting in catastrophic engine failure. 

Lower cylinder 

head portion 

Barrel 

Upper cylinder 

head portion 

Figure 1. Photograph of a fractured cylinder assembly. 

Beginning in 2004, ECi and the FAA issued several bulletins and directives to address 

these fatigue failures. After 34 reported fatigue failures of ECi cylinders, the FAA issued 

AD 2004-08-10, effective May 2004, to require replacement of certain ECi cylinder assemblies 

on TCM model 520 and 550 series engines. The AD identified a manufacturing discrepancy that 

occurred between September 2002 and May 2003 (S/N 1044-7708), which resulted in an 

inadequate cylinder head wall thickness and an over-hardened condition that would reduce the 

fatigue strength of the aluminum cylinder head. 

In August 2006, ECi issued Mandatory Service Bulletin (MSB) 06-2 instructing operators 

to perform repetitive inspections for leaks and cracks on cylinder assemblies between S/N 7709 

and 33696 and to replace any discrepant cylinders. Affected assemblies were produced between 

September 2002 and November 2005 with inadequate cylinder head wall thickness on the 

exhaust side. At least 21 head separations have been reported for this group of cylinders, and the 
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NTSB has investigated several of these, including those documented in NTSB case number 

ENG07SA033. The fatigue initiated on the exhaust side of the cylinder head, between the 14th 

and 16th cooling fins, and propagated inwards toward the valve seat. The FAA issued Special 

Airworthiness Information Bulletin (SAIB) NE-07-09R1 in March 2007, detailing the 

importance of performing the inspections called for in ECi MSB 06-2, but did not require the 

inspections. 

Cylinder head 

Cylinder barrel 

Figure 2. A sectional view of an ECi cylinder head and barrel, showing the location of fatigue 

cracking (yellow line) and shrink bands (red and green arrows). 

ECi has also informed the NTSB of at least eight cylinder head fatigue failures in the 

group of cylinder assemblies produced between October 2005 and October 2009 

(S/N 33697-52884) for installation on TCM engines that are currently not covered by any 

corrective bulletin or directive. Including these eight failures, at least 29 cylinder head fatigue 

failures have been reported and confirmed for new ECi cylinder assemblies with serial numbers 

between S/N 7709 and 52884 for installation on TCM engines. 

NTSB and FAA representatives formed a task force in 2005 to study fatigue failures of 

cylinder heads, which at that point included domestic and foreign failures. In 2006, the task force 

visited several facilities, including ECi, and observed the entire manufacturing process, from 

casting of the cylinder heads to cylinder assembly. The NTSB continued examining failed 

cylinders and updating the FAA’s aircraft certification office responsible for oversight of ECi. 

Following a meeting of NTSB, FAA, and ECi representatives in October 2006 to discuss the 

cylinder head fatigue failure issue, ECi designed and manufactured a fatigue test fixture that 
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simulates the cylinder head temperature and pressure cycles experienced by a cylinder on an 

operating engine. After running numerous tests, ECi changed the manufacturing process for its 

cylinder assemblies in October 2009 to provide an increased interference fit at the shrink band 

and between the cylinder head and the cylinder barrel threads but remaining within the limits of 

the approved design. 

During a meeting in January 2011 between ECi, the FAA, and the NTSB, ECi prJduced 

data on the cylinder assembly failures and recommended that the FAA issue an AD to mandate 

inspection and replacement of any discrepant cylinders; however, the FAA has not taken the 

recommended action for those cylinders not currently covered by an AD. Since the design 

improvement in October 2009, there have been no reported cylinder head fatigue failures on ECi 

cylinder assemblies installed on TCM model 520 and 550 engines. Although ECi's changes to 

the manufacturing process may increase the fatigue strength of new production cylinder heads, a 

large population of potentially discrepant cylinder assemblies remains in service without any 

required corrective action. 

Therefore, the National Transportation Safety Board makes the following 

recommendation to the Federal Aviation Administration: 

Require repetitive inspection of Engine Components, Inc. cylinder assemblies 

produced between May 2003 and October 2009 (serial numbers 7709 through 

52884) installed on Teledyne Continental Motors model 520 and 550 engines 

and removal of these cylinder assemblies once they reach the engine 

manufacturer's recommended normal time (hours) in service between overhauls. 

(A-12-7) 

In response to the recommendation in this letter, please refer to Safety 

RecommendationA-12-7. If you would like to submit your response electronically rather than in 

hard copy, you may send it to the following e-mail address: correspondence@ntsb.gov. If your 

response includes attachments that exceed 5 megabytes, please e-mail us asking for instructions 

on how to use our secure mailbox. To avoid confusion, please use only one method of 

submission (that is, do not submit both an electronic copy and a hard copy of the same response 

letter). 

Chairman HERSMAN, Vice Chairman HART, and Members SUMWALT, ROSEKIND, 

and WEENER concurred in this recommendation. 

By: Deborah AP. Hersman 

Chairman